I’ve heard a lot about how younger patients can get knee replacements sooner than later now. I was told that most implants last 15 years (or more). I’m seriously thinking about going for it. What happens to the folks whose knees don’t hold up?

That’s a good question and one that every patient should consider. The expectation is that your implant will last 10 to 15 years with moderate activity. It’s not designed to stand the rigors of multiple marathons — and most people in need of a knee replacement aren’t in that category anyway.

But doctors may define the success or failure of an implant differently. So that’s an important thing to look at. For example, some surgeons consider the implant a success if it doesn’t fail. That sounds rather simplistic.

What it means is that if the implant doesn’t need to be removed, replaced, or revised in some fashion, then it was a success. Infection, implant loosening, and bone fracture or fracture of the implant are the most common reasons for implant revision.

But patients may use a different measuring stick. They come into the surgery with severe, disabling knee pain. That’s why they wanted a new knee. They expect to come out of it pain free and able to engage in some of their former activities — or at least be more active. That may mean being able to walk unrestricted, ride a bike, go on a hike, dance, swing a golf club, or hit a few games of tennis.

What many people find is that they still experience mild-to-moderate levels of pain. A small number of folks report severe pain. Only about one-third of the patients providing information on pain in studies conducted are actually pain free.